Creating a compatible community of marine fish

Creating a Compatible Community of Marine Fish

One of the most convenient aspects of keeping marine fish is the fact that, unlike many tropical freshwater fish, which differ in their environmental requirements, most marine species are found in similar conditions in the wild.

This means that fish that would be separated from the oceans in the wild can be kept alongside each other in the aquarium, as long as factors such as territorial and dietary requirements are taken into account.

Unlike freshwater fish, marine species likely to be kept in the aquarium are almost always aggressively territorial. This means that individuals of the same species are just as likely to fight in an aquarium as they would be in the wild, unless they are already paired or the correct sizes/sexes to do so.

Such territorial aggression is the limiting factor for population density in the wild and is the reason that young fish are the best choice for the aquarium, as their harvesting has little impact on healthy reef fish populations. An increasing number of fish are being bred in captivity, and as well as being hardier and less stressed than their wild counterparts, they tend to be less aggressive.

When deciding which fish to keep in your aquarium, a number of factors are important:

  • Will this fish feed on invertebrates or tank mates?
  • Will this fish bully or be harassed by other inhabitants?
  • Will this fish outgrow the setup in question?
  • Is this fish suitable for life in an aquarium?

Although other factors may be of concern, these are the most important and can be seen to be behind most of the unsuccessful attempts to introduce new fish.

Many popular fish use the most numerous food resource found in their natural habitat: marine invertebrates.

Some are very unselective and will sample most organisms including shrimp, anemones and corals. These species are usually easy to feed but are never suitable for reef tanks.

Other fish are superbly adapted to feed on smaller fish and will gobble up the most suitable individuals they find, as do freshwater predators. These fish are often available as very young individuals and find their way into community tanks, where the other tankmates eventually become lunches as they grow.

A common mistake is to add territorial species such as Damsels to new tanks due to their tolerance of contamination as the system matures during the early stages. This results in difficulties in adding less aggressive specimens to the damsel’s territory, something that would not be tolerated in the wild and is not welcome in your aquarium’s artificial reef.

A better way to mature any marine tank is to add live rock to support the biological load and introduce the least aggressive specimen first, once water quality allows.

More aggressive individuals can be added last and can usually establish a territory alongside established fish with much less interruption.

The task during the early stages can determine the order in which your community should be established. Due to the territorial nature of reef fish, avoid placing species with similar colors or markings in the same tank, as they will typically collide in living space.

Members of closely related species can also be poor choices, as they are likely to require identical niches and fight just as much as two individuals of the same species. Another combination prone to problems is mixing species with the same feeding pattern; some Tangs and Blennies, for example, can be aggressive toward other algae-eating fish.

Many commonly available marine fish will grow to large sizes and can be purchased by the unwary before home aquariums grow larger.

Dragon, Clown and Twinspot wrasses (Novaculichthys and Coris) are often seen as small juveniles that can grow much larger than 30cm and become very disruptive. Lionfish (Pterois) are equally capable of growing and eating a wide range of tank mates, even ‘dwarf’ lionfish (Dendrochirus) can grow up to 20cm but prefer a diet of crustaceans. Panther or polkadot groupers (Chromileptes) reach 60 cm or more in common with many other frequently seen members of this group.

Size is not the only limiting factor in successfully keeping marine fish, as in the proper setup many of these large fish can be successfully kept and will live long and healthy lives.

More problematic are species adapted to diets that cannot be duplicated in captivity, such as butterflyfish (Chaetodon), filefish (Oxymonacanthus), and blennies (Exalias) that feed on corals, or those whose requirements are not well understood. such as Sweetlips (Plectorhinchus), some Batfish (Platax), and Goatfishes (Parupeneus). These fish should be avoided as they are not suitable for aquarium life and should not be removed from the wild.

Another group that deserves mention are those species such as Dragonets (Synchiropus) that can only be kept when nutrition problems are resolved. These fish should be kept in established aquaria with healthy populations of amphipods and copepods to allow for natural feeding behavior.

Similarly, seahorses (Hippocampus) are difficult and time consuming fish to feed and should not be housed with species that out-feed them. Due to pressure on wild populations, only captive-bred seahorses should be selected.

Cleaner wrasses (Labroides) are also difficult to keep and are only suitable for aquariums that house communities of large fish more commonly seen in public facilities. Their removal from reefs also harms the health of wild fish. Neon gobies (Gobiosoma) are an excellent alternative and captive bred specimens are the most commonly available.


In short, a well-selected marine fish community should consist of a variety of colors and patterns, with similar levels of aggression and adult sizes. Individuals should be added in increasing order of aggression and species should be researched prior to selection to ensure suitability.

All fish should be fed and healthy prior to purchase and while not essential, a quarantine tank can be a very helpful resource in ensuring a long and healthy life for your aquatic pets.

As tempting as it may be, never buy sick fish out of sympathy, as it simply rewards the wrongdoing of the supplier in question. From Acuario3web we only recommend selecting high quality populations bred in captivity or captured with nets from sustainable sources.

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